1. Field of the Invention
The present invention relates to a process for the degradation of a viscous microbial polysaccharide formulation.
2. Description of the Prior Art
The process concerns in particular the degradation of polysaccharide formulations which are, inter alia, employed as well completion fluids, workover fluids and/or fluids used to drill oil or gas production wells. The polysaccharides are employed in these fluids to increase their viscosity. Increased viscosity reduces fluids loss and increases the solids carrying capacity of the fluid. In order to achieve acceptable productivity levels the viscous polymer solution, which has invaded the reservoir-formation during the completion, workover and/or drilling operation, must be degraded as quickly as possible. This is usually achieved either by incorporating acid into the fluid itself or by an acid post flush which should degrade any remaining fluid which might impair the permeability of the formation in the vicinity of the wellbore. It has now been found that polysaccharide formulations can be degraded unexpectedly fast when acid is added if those formulations contain high levels of certain salts. Further investigation has revealed that under such conditions the transition temperature of the biopolymer has decreased substantially. The transition temperature, Tm, is the temperature above which biopolymers undergo a change to a less ordered state as is explained in a paper of the Society of Petroleum Engineers of AIME (SPE 12085) which was presented at the 58th Annual Technical Conference and Exhibition held in San Francisco, Calif., Oct. 5-8, 1983. It is striking that the fast degradation of the biopolymer is in particular marked when the temperature at which acid is added is close to Tm. Therefore it is a great advantage that the present invention opens the possibility of controlling the transition temperature such that it comes close to the temperature of the oil and/or gas reservoir(s) which is usually the bottomhole temperature of the well. Thus the present process makes it possible that biopolymer e.g. in workover and completion brines or drilling fluids which are not used anymore can be quickly degraded.